1. Field of the Invention
The present invention relates to a pilot control valve that achieves a continuous and consistent pumping rate for a reciprocating pump. More particularly, the pilot control valve of the present invention relates to a pilot control valve that controls the flow of control fluid to a piston, valve or the like to drive a reciprocating device such as a chemical or glycol injection pump. The pilot control valve of the present invention controls such flow through a pneumatic valve mechanism with the use of a reduced number of moving parts and a single movable valve member.
2. General Background
There are various devices known for controlling reciprocating pumps. Previous designs have used a separate pump and pilot assembly such as that illustrated in U.S. Pat. No. 2,990,910, issued to G. O. Kimmell and entitled "Apparatus And Method For Circulating Controlling Liquids and Gas-Liquid Systems". Other devices have used springs, nuts, bolts or other components for the backstroke of the piston, but these components often fatigue or fail under fluid pressure. These prior art devices were overcome by the pilot control valve inventions disclosed in U.S. Pat. No. 4,593,712, issued to Anthony J. Quartana, III, entitled "Pilot Control Valve" which issued on Jun. 10, 1986, and U.S. Pat. No. 4,776,773, issued to Anthony J. Quartana, III, entitled "Pilot Control Valve for Controlling the Pumping Rate of an Injection Pump" which issued on Oct. 11, 1988.
The pilot control valve disclosed in U.S. Pat. No. 4,593,712 includes a first or "leading" valve member and a second or "following" valve member coaxially positioned with respect to each other within a valve body to control the communication of control fluid to a piston included with an injection pump to initiate movement of the piston between its first or "downstroke" position and its second or "upstroke" position to drive the injection pump. In response to control fluid supplied to the valve body, the first valve member moves from its first or "downstroke" position to its second or "upstroke" position. The movement of the first valve member to its second position allows the control fluid to act on the second valve member causing it to move from its first or "downstroke" position to its second or "upstroke" position. When the second valve member reaches its second position, the piston of the injection pump returns to its first position. The return of the piston to its first position allows control fluid to cause the movement of the first valve member from its second position to its first position which then allows control fluid to cause the movement of the second valve member from its second position to its first position. As the second valve member returns to its first position, control fluid causes the piston and a rod attached to the piston to move upwardly toward its second position. As the piston moves upwardly, the end of the rod on the piston engages the first valve member and drives the first valve member upwardly to its second position and the process is repeated over and over. In this manner, the reciprocating pump achieves a consistent pumping rate.
The pilot control valve disclosed in U.S. Pat. No. 4,776,773 includes a first or "leading" valve member movable between a first and second position, but eliminates the use of a second or "following" valve member coaxially positioned with respect to the first valve member. Instead, a second or slide valve member is loosely mounted on the first valve member and is movable between a first or "downstroke" position, an intermediate position and a second or "upstroke" position. When in its first position, the second valve member allows communication of the control fluid to the piston included with the injection pump to initiate movement of the piston from its first or "downstroke" position to its second or "upstroke" position. As the piston moves upwardly, the end of the rod attached to the piston engages a surface of the first valve member to initiate its movement from its first to its second position. As the first valve member moves from its first to its second position, the first valve member moves the second valve member from its first position to its intermediate position and then to its second position. When in its intermediate position, the second valve member blocks the communication of control fluid to the piston and the piston is no longer driven upward. Finally, in its second position, the second valve member allows control fluid to return the piston to its first position and to move the first valve member from its second position back to its first position. This process is repeated over and over to achieve a consistent pumping rate.
Although the pilot control valves disclosed in U.S. Pat. No. 4,593,712 and U.S. Pat. No. 4,776,773 overcome the prior art devices, there is still a need in the industry for a pilot control valve that further reduces the number of moving parts in the valve mechanism to improve reliability and resistance to wear. The pilot control valve of the present invention improves the reliability of the prior art pilot control valves by providing a pilot control valve that controls the communication of control fluid to a piston included with a reciprocating device using pneumatic valve control rather than a mechanical control mechanism and requiring a reduced number of moving parts. The pilot control valve of the present invention eliminates the use of the second coaxial valve member disclosed in U.S. Pat. No. 4,593,712 and the second slide valve member disclosed in U.S. Pat. No. 4,776,773 and provides for the complete control of the upstroke and backstroke of the piston in a pneumatic manner with a single movable valve member.